1. Field of the Invention
The present invention relates to optical systems using a beamsplitter. More particularly, the present invention relates to an optical system including a beamsplitter, such as a beamsplitter prism, for transmitting or reflecting cylindrical waves without magnification.
2. Description of the Related Art
A beamsplitter divides an incident beam into two parts, with one part being transmitted and the other part being reflected. Normally, a beam splitter is placed at a 45xc2x0 angle to the incident beam in order to reflect one part of the light at a 90xc2x0 angle, and to allow another part of the light to pass through.
In addition, a beamsplitter can be used to combine two light beams (forming an apparent composite image) if the beamsplitter is positioned at an intersection of the two paths at a specific angle to each of the paths.
There are many types of beamsplitters, which include, for example, partially transparent metal films, plate-type beamsplitters having an optically symmetrical structure, prism-type beamsplitters, and beamsplitters which can reflect linear polarization and transmit orthogonally polarized light.
Of the beamsplitters mentioned above, beamsplitter prisms are often used in devices such as interferometers and many types of scanners.
In general, a beamsplitter prism is cubical and has a thin layer of semi-reflecting material placed diagonally across its interior. Approximately one half of the light entering one of the faces of the beamsplitter prism is reflected by the semi-reflecting material so that it exits an adjacent face. The rest of the light is transmitted by the layer and passes through the opposite face.
Cylindrical waves are often implemented in imaging devices like scanners and copiers to image a line-source onto a line image, which means that these waves will pass through beamsplitter prisms.
However, the behavior of cylindrical waves are more complex than that of, for example, plane waves. Cylindrical waves pose a problem in that the transmission of a cylindrical wave emanating from a line undergoes distortion when passing through a conventional beamsplitter prism. In other words, the cylindrical wave appears to emanate from a location different than the actual location. As a result of this distortion, the cylindrical wave is no longer cylindrically shaped after exiting the beamsplitter prism.
The amount of distortion which is introduced on a cylindrical wave by the beamsplitter prism is dependent upon, inter alia, the type of material from which the prism is constructed and the size of the prism.
Accordingly, if a beamsplitter prism is used in conjunction with a backscattering detector for measuring backscatter from a, particle system, the amount of distortion introduced by the beamsplitter prism must be taken into account when calculating the scattering angle. This calculation causes the design of the detector to be more complex.
In addition, the distortion of the cylindrical wave caused by the beamsplitter prism may also affect the quality of scanning devices.
Accordingly, it is an object of the present invention to overcome the problems of the prior art.
To this end, according to the present invention, there is provided a beamsplitter prism for transmitting and reflecting cylindrical waves without magnification, the beamsplitter comprising:
at least first and second surfaces arranged opposite each other; and
a semi-reflecting layer diagonally arranged from a lower portion of the first surface to an upper portion of the second surface,
wherein the first and second surfaces have a cylindrical shape, the first surface has a smaller radius than the second surface, and the first and second surfaces form two concentric cylinders, whereby a cylindrical wave which strikes the first surface passes through the semi-reflecting layer and exits through the second surface without the beamsplitter prism introducing distortion to the cylindrical wave.
In an embodiment, the beamsplitter may further comprise a third surface having a substantially planar shape and being substantially orthogonal to the first and second surfaces along an upper surface of the beamsplitter prism, whereby a plane wave which strikes the third surface is at least partly reflected by the semi-reflecting layer and exits through the first surface.
According to an aspect of the invention, the first surface may have a radius of curvature R1 which is equal to a distance from the first surface to a point P that represents a point from which the cylindrical wave emanates.
In addition, the second surface may have a radius of curvature R2 which is equal to a distance from the second surface to a point P that represents a point from which the cylindrical wave emanates.
According to another aspect of the invention, the third surface may be bent for counteracting a bending effect on a plane wave by the first surface.
In addition, a shape of the beamsplitter prism may be substantially cubical, and the first and second surfaces may constitute cylindrical lenses attached to opposite sides of the beamsplitter prism.
Alternatively, the first and second surfaces may constitute cylindrical lenses formed in their respective surface.
The first and second surfaces may constitute a plano-concave lenses, or a plano-convex lenses.
According to another embodiment of the present invention, there is provided a beamsplitter prism for transmitting and reflecting cylindrical waves without magnification, comprising:
at least first and second surfaces arranged opposite each other;
a third surface arranged substantially orthogonal to the first and second surfaces; and
a semi-reflecting layer diagonally arranged from a lower portion of the first surface to an upper portion of the second surface;
wherein the first and third surfaces have a cylindrical shape, the first surface has a smaller radius than the third surface, a shape of the first surface and an image of the third surface form concentric cylinders, whereby a cylindrical wave, which strikes the first surface, semi-reflects off the semi-reflecting layer and exits through the third surface, without the beamsplitter prism introducing distortion thereto.
According to an aspect of the invention, the third surface may have a radius of curvature R1 which is equal to a distance from the first surface to a point P that represents a point from which the cylindrical wave emanates.
Additionally, the third surface may be bent to counteract a bending effect on a plane wave from the first surface so that the a shape of the plane wave bends after striking the third surface and is corrected by subsequently exiting through the first surface.
The second surface has a radius of curvature R2 wherein R2=R3+R4, where R3 is equal to a distance from a lower edge of the semi-reflecting layer to point P, R4 is equal to the distance along an upper edge of the first surface to the lower edge of the semi-reflecting layer, and point P represents a point from which the cylindrical wave emanates.
The shape of the beamsplitter prism may be substantially cubical, and the first and second surfaces may constitute cylindrical lenses attached to orthogonal sides of the beamsplitter prism.
Alternatively, the first and second surfaces each may constitute a cylindrical lens formed in a respective surface.
In another aspect of the present invention, at least one of the first and second surfaces may constitute a plano-concave lens.
In yet another aspect of the present invention, at least one of the first and second surfaces may constitute a plano-convex lens.